Query based on multiple where clauses in firebase - 


{ "movies": {     "movie1": {         "genre": "comedy",         "name": "as gets",         "lead": "jack nicholson"     },     "movie2": {         "genre": "horror",         "name": "the shining",         "lead": "jack nicholson"     },     "movie3": {         "genre": "comedy",         "name": "the mask",         "lead": "jim carrey"     }   }    }

i firebase newbie. how can retrieve result data above where genre = 'comedy' , lead = 'jack nicholson' ?

what options have? in advance.

using firebase's new query api, might tempted try this:

// !!! not work !!! ref   .orderby('genre')   .startat('comedy').endat('comedy')   .orderby('lead')                  // !!! line raise error !!!   .startat('jack nicholson').endat('jack nicholson')   .on('value', function(snapshot) {        console.log(snapshot.val());    });

but @robdimarco firebase says in comments:

multiple orderby() calls throw error

so my code above not work.

i know of 3 approaches work.

1. filter on server, rest on client

what can execute 1 orderby().startat()./endat() on server, pull down remaining data , filter in javascript code on client. 

ref   .orderby('genre')   .equalto('comedy')   .on('child_added', function(snapshot) {        var movie = snapshot.val();       if (movie.lead == 'jack nicholson') {           console.log(movie);       }   });

2. add property combines values want filter on

if isn't enough, should consider modifying/expanding data allow use-case. example: stuff genre+lead single property use filter. 

"movie1": {     "genre": "comedy",     "name": "as gets",     "lead": "jack nicholson",     "genre_lead": "comedy_jack nicholson" },...

you're building own multi-column index way , can query with:

ref   .orderby('genre_lead')   .equalto('comedy_jack nicholson')   .on('child_added', function(snapshot) {        var movie = snapshot.val();       console.log(movie);   });

david east has written library called querybase helps generating such properties.

you relative/range queries, let's want allow querying movies category , year. you'd use data structure:

"movie1": {     "genre": "comedy",     "name": "as gets",     "lead": "jack nicholson",     "genre_year": "comedy_1997" },...

and query comedies of 90s with:

ref   .orderby('genre_year')   .startat('comedy_1990')   .endat('comedy_2000')   .on('child_added', function(snapshot) {        var movie = snapshot.val();       console.log(movie);   });

this can work multiple values, can range filter on last value in composite property.

3. create custom index programmatically

yet alternative we've done before new query api added: create index in different node:

  "movies"       // same structure have today   "by_genre"       "comedy"           "by_lead"               "jack nicholson"                   "movie1"               "jim carrey"                   "movie3"       "horror"           "by_lead"               "jack nicholson"                   "movie2"

there more approaches. example, answer highlights alternative tree-shaped custom index: https://stackoverflow.com/a/34105063


Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj
Read more

performance - Why is XCHG reg, reg a 3 micro-op instruction on modern Intel architectures? -

i'm doing micro-optimization on performance critical part of code , came across sequence of instructions (in at&t syntax): add %rax, %rbx mov %rdx, %rax mov %rbx, %rdx i thought had use case xchg allow me shave instruction , write: add %rbx, %rax xchg %rax, %rdx however, dimay found agner fog's instruction tables , xchg 3 micro-op instruction 2 cycle latency on sandy bridge, ivy bridge, broadwell, haswell , skylake. 3 whole micro-ops , 2 cycles of latency! 3 micro-ops throws off 4-1-1-1 cadence , 2 cycle latency makes worse original in best case since last 2 instructions in original might execute in parallel. now... cpu might breaking instruction micro-ops equivalent to: mov %rax, %tmp mov %rdx, %rax mov %tmp, %rdx where tmp anonymous internal register , suppose last 2 micro-ops run in parallel latency 2 cycles. given register renaming occurs on these micro-architectures, though, doesn't make sense me done way. why wouldn't register renamer
Read more

jquery - Responsive Navbar with Sub Navbar -

good day, forgive me nav vocabulary not best. if question confusing apologize. i'm working on navigation bar needs centered on page @ 768px , above. items in nav open (or perhaps toggle) subnav lives directly below. these nav should appear centered on page. i have been able work through responsive portion of nav bar, having main items align vertically , sub nav menu of each item roll out below, , gave them indent separation. working well. however, issue not responsive side, behavior @ width greater 768px. happens toggling menu's sub navigation pushes other main items down page below sub nav. here's code: $(document).ready(function () { //stick in fixed 100% height behind navbar don't wrap $('#slide-nav.navbar-inverse').after($('<div class="inverse" id="navbar-height-col"></div>')); $('#slide-nav.navbar-default').after($('<div id="navbar-height-col"></d
Read more